Thermostatic snap switch



Dec. 23, 1952 J. E. KUMLER 2,623,138

THERMOSTATIC SNAP SWITCH Filed Nov. 1, 1947 2 SHEETSF-SHEET 1 Fig.1

F 1: Z INVENTOR,

JOSEPH EDWARD HUMLER im 7% M444 g Hrs ATTORNEY Dec. 23, 1952 J. E. KUMLER 2,623,138

THERMOSTATIC SNAP SWITCH Filed Nov. 1, 1947 2 SHEETS--SHEET 2 Fig.3

INVENTOR. JOSEPH EDWARD KUMLER.

HIS ATTORNEY Patented Dec. 23,, 1952 THERMOSTATIC SNAP SWITCH Joseph Edward Kumler, Columbus, Ohio, assignor to Ranco Incorporated, Columbus, Ohio, a corporation of Ohio Application November 1, 1947, Serial No. 783,573

2 Claims.

This invention relates to control apparatus, and more particularly to switch for protecting an electric motor against overload.

One of the objects of this invention is to provide for an electric motor a circuit breaker adapted to open the motor circuit in response to a rise in temperature within the motor housing and to reclose the circuit when the temperature falls below a predetermined value.

Another object of this invention is to provide an overload protector of the character described which is compactly assembled within a small, light weight housing adapted to be mounted .directly upon the motor frame for response to 1 temperature changes therein caused by either excessive current values alone, or an excessive temperature rise, or by a combination of these conditions causing an excessive temperature rise.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred forms of embodiments of the invention are shown.

In the drawings:

Fig. 1 is a top elevational view of the housing with the outer cover plate removed and illustrating the starting relay with its contacts in the open position, the overload protecting mechanism being shown with the contacts in the closed position;

Fig. 2 is a partial sectional and elevational view taken substantially on the line 22 of Fig. 1 showing the overload protecting mechanism in detail;

Fig. 3 is a view similar to Fig. 1 illustrating the starting relay with the contacts in the closed position, the overload mechanism also being illustrated with the contacts in the closed position; and

Fig. 4 is another view similar to Fig. 1 and illustrating the starting relay contacts open, the overload contacts also being shown open.

Referring further to the drawings, the control apparatus illustrated in Fig. 1 comprises in general a receptacle 2B of plastic material such as Bakelite. This receptacle is provided at each side thereof with an outwardly projecting lug 2|, 22 through which is formed an aperture 23, 2d for receiving the mounting bolts 25 and 26 shown in Fig. 2. The receptacle 20 is provided with a dividing wall 28a and forwardly extending flanges 281) on three sides to provide a terminal housing 280. The housing 200 is closed in the front with a removable plate 21. Flanges 30 extend rearward from the dividing wall 20a to provide a switch mechanism housing 2911. A cup 3| is formed with an inwardly curved rear wall 32 adapted to fit closely in contact with the outside of the curved outer wall 35 of, for example, the frame of an electric motor as near the location of the windings as possible. The receptacle 20 forms a closure for the open end of cup 3|. Heat developed within the motor housing or frame 35 from overload conditions or otherwise is thus transmitted directly from the cup to the housing Zlld. The rear wall 32 of the cup is fastened to the wall 35 by means of welding, brazing, or screws if preferred; the receptacle 20 is connected to the cup by the screws 25 and 26 as shown. It is to be noted that this housing and cup construction provides for mounting the overload control apparatus in a position spaced relative close to the wall 32 as seen in Fig. 2.

The startihg apparatus and overload control mechanism in general are both supported upon a common frame ii] within housing 2001. This steel frame is formed to provide at one end an L-shaped supporting portion 4| within which a magnetic coil 42 is mounted, one end of the coil being secured thereto as by welding. The outer end of portions 4| is turned inwardly and provides an ear 63 through which one of the starting apparatus adjusting screws 44 is received. The other end of the frame forms a supporting portion 51 through which a second of the start ing apparatus adjusting screws 52 and the overload adjusting screw 53 are mounted. Also formed as an integral part of the central portion :35 of the frame is the depending portion 54. This portion of the frame is bent at right angles to the central portion and has an end thereof upwardly turned (as viewed in Fig.1) to form a support 55, upon which parts of the overload control mechanism are mounted as described hereafter.

The frame is supported within the housing 200, in a position out of contact with th walls thereof. Thus it is not substantially affected by stress or strains imparted from any movement of the housing walls caused by expansion or contraction thereof. To support the frame in this position ported solely by the bimetal strip Ital.

3 it is mounted on a small raised pad fit, Fig. 2, which is formed as an integral part of th housing wall. The pad is approximately of an inch in width and about inch in length. A pair of screws 6i and 62, Figs. 1, 2 and '7, serve to hold the frame in position on the pad.

Referring further to the starting apparatus, one nd of a beryllium-copper armature spring 65 is connected to the underside (as viewed in Fig. 1) of the supporting portion 5| of the frame. The spring is formed with the offset portion 68 having one nd thereof pierced to receive a silver contact 19 as shown in Fig. 1. One end of a steel armature is Welded to spring 65 at substantially the mid-point of the latter by a welding plate I3. The armature is formed with an off-set curved portion through which portion 88 of the spring extends so that the contact Iii-lies below the armature 12 (as viewedin Fig. 1). The free end of the armature 'IZ is provided with a rectangular shaped slot (not shown) which is positioned directly over, or so as to register with and permit the end of th central steel corett of coil 42 to project through when the starting apparatus is closed as seen in Fig. 3.

To complete the coil assembly there is pro vided at each end a fiber insulating disc SI and 32. One end of the coil is connected by the copper lead wire 83 to the terminal outlet 84 formed through the front wall of the housing. I

This terminal outlet is in turn connected through a small screw 85 and lead wire to the main winding of the motor.

A brass terminal member so is mounted adjacent the front wall of the housing, 1. One endof this terminal is extruded and tapped to receive a screw 9! connecting a lead line to a starting winding of a motor. The other end of terminal 59 is bent upwardly (as viewed in Fig. 1)

at right angles to form an arm 95 which carries a silver contact 925. Thus the contacts F0 and 96 are positioned so as to move into engagement when the starting apparatus is closed as illus trated in Fig. 3, the armature l2 moving to the closed position when the coil as is energized.

The overload control mechanism comprises in general a bimetal strip Ill-3 having one end thereof welded to. the underside of the supporting portion M of the frame. Toggle mechanism is sup- I'he toggle mechanism includes an elongated T-shaped toggle arm :82. The free end of this strip is welded to substantially the portion of the main leg of the T-shaped toggle arm I532, Figs. 1

and 2, of stainless steel, or other non corrosive alloy. The toggle mechanism also includes an elongated leaf spring Hi5. Springmember I35 isbifurcated to provide spring tines or spring members H36 and It'd, which lie along opposite sides of the main leg of the toggle arm. The ends of the tines are secured by rivets I58 and Ht, to the left end (as viewed in Fig. 2) of the opposed portions of the cross leg of the toggle arm iEiE. From the free end of the spring I35 a short, flexibl spring arm i i i extends inwardly between the tines Idfi and is? The inner end of arm III is in turn received within a v notch H2 formed in the end of the toggle arm Hi2. A silver contact I it is secured to the free (right) end of spring I85.

Compactness of essential, particularly when the control is applied to fractional horse power electric motors. it is also essential that the mechanism be simple in construction and that it be manufactured at a low cost. Although compactness and simplicity are essential, sacrifice cannot be made on the length of the bimetal strip. It must b sufficiently long to function with precision and must be of suflicient cross-sectional area to carry not only the normal load but also abnormal loads to which the motor is occasionally subjected.

By connecting the movable (right) end of th bimetal strip its to the toggle arm I82, in the manner herein disclosed i. e. solely at a pointspaced longitudinally from that end of the toggle arm which is connected with the spring, as for example intermediate the. rivets It!) and the fulcrum point on V-notch II 2, toggle ,arm I82 will function as a lever of substantially th third order when movement is imparted thereto by the strip I88, 1. e. the component of forces of thetension members I96 and It! and the com- ,pressionmember III, tend to hold the left end of toggle arm- I {)2 stationary while swinging movement-isimparted to the right end of toggle arm I532 by Stri I06. Thus the movement of V-notch -I I2 is greater than a given movement of the free end of bimetal strip I00. This is readily apparent from Figs. 3 and 4. Consequently a small movement of the free end of strip I00 will besufficient to .movethe notch I I2 from one side of and throughitsdead center position. Also by soconnecting the strip IDE! to the toggle arm IE2, the effective length of strip I00 isincreased while compactness is obtained. Furthermore, since by the particular attachment ofthe bimetal strip with the toggle arm I02, said arm functions as a toggle lever wherein the notch .I I2 thereof movesin a greater radiusthan the right end of bimetal strip IMJ. Since, in carrying out its function, the movement of the free end of the bimetal strip is small comparedto its length, this strip can be fabricated from sufficiently heavy and sturdy material and therefore will not be damaged by generation of heat to which it is normally and abnormally subjected.

To complete the circuit from one side of the power supply line, a lead line I2I is brought in through the screw I22 and the inlet terminal 23. This. terminal is formed with a flat strip of dead soft copper wrapped to form an outer turn I25 extending substantiallyaround an inner rin I27. Through the center of this ring extends a brass bushing I38 which extends, in turn, up through the support 55 of the frame. Fiber insulators I3I, I32 and I33 are provided to insulate the bushing from the frame, the upper end of the bushing having a shoulder while the lower end thereof is erimped over to retain; these members imposition. A brass screw I35 isreceived within the bushing and its head provides a support for the silver contact I36. Thus when the overload mechanism is closed, as in Figs..1 and 3, the contacts H3 and I36 engage one another.

,A pair of dummy terminals Mil and .I4I area1so provided. Through these terminals auxiliary equipment as desired can be connected.

Normally the starting contacts I6 and SIB- are openand the overload contacts H3 and I36 are closed. Th current can then flow from the supply source through terminal I23, through the toggle spring I65 and toggle I62 and bimetal I00 to theframe Since the contacts In and 96 are open, the current flows from the frame through the coil 42, lead 83, terminal 84 to the main (running) winding of the motor. Thus the coil E2 is energized and the armature I2 isattracted toward the coil, closing the contacts ,Ill

and 96 as seen in Fig. 3. Current can then flow from the frame 40 by way of-the armature 12,

contacts 10 and 96, through terminal 90 to th to close the contacts It and 96 at a predetermined current value of about 6 amperes and to open when the current value drops to approximately 5.5 amperes. This calibration is effected by first adjusting the screw 52 i. e., raising or lowering it until the tension of sprin 65 is just sufiicient for a magnetic pull induced in coil 42 when energized by the flow of more than 5.5 amperes to maintain the armature attracted to the contact closing position. When less than 5.5 amperes flows in coil 42, the spring 65 will pull the armature away from the coil. Screw 44 is then adjusted until the armature is so deflected that when the current through the coil 42 reaches 6 amperes, the magnetic pull is suincient to overcome the spring tension and the armature will move to the contact closing position.

In connection with the operation of the overload control mechanism to open the circuit and stop the motor, it is to be noted that operation is effected by one or more of three sets of conditions. That is, it operates if the current alone becomes excessive or dangerously high with respect to the windings. It will also operate if the temperature alone within the motor housing or frame rises beyond a predetermined point. Thirdly, it operates if there is a combination of excessive current and rise in temperature. The bimetal I will deflect with a change in the temperature regardless of how derived. Thus anyone of the conditions enumerated causes the bimetal to deflect. Such deflection is in turn sufficient to move the connected toggle arm I02 until the tripping points of the toggl and spring I05 are in line, at which time the toggle trips open, as shown in Fig. 4, and the contacts H3 and I36 are opened with a snap action. This opening of the contacts breaks the main line circuit. Since under this condition no current can flow, the ambient temperature within the housing drops and the bimetal cools whereby it deflects in the opposite direction. This brings the tripping points again into line and the toggle snaps the contacts H3 and I36 closed, current can then flow and the starting cycle is repeated. It will be apparent that if the same condition causing the rise in temperature still exists, or again develops, the overload mechanism will function and repeat cycling until the condition in question is removed.

The overload control mechanism is adjusted in the following manner. If, for example, it is desired that the overload cycle when the ambient temperature within the housing reaches approximately 205 F., the screw !35 carrying the contact I35 is raised or lowered ntil that temperature is just sufiicient for the bimetal to deflect enough for the tripping points of the toggle to be brought into line and open i. e., move contact H3 out of engagement therewith. If, under the same conditions it is desired that the overload cycle to the reset or closed position when the temperature drops to about 165 F., then screw 53 is adjusted until that temperature causes deflection of the bimetal sufficient to cause the toggle tripping points to be brought into line again and snap the contacts closed.

From the above description, it will be apparent that there is provided a combined starting relay and overload protector device such that the temperature of the motor windings are prevented from rising to a dangerous level. In the construction shown the overload control mechanism repeats its cycling until the cause of the rise in temperature has been corrected, or until the main line switch is open. The starting relay and overload control mechanism is designed for mounting directly against the dome or frame enclosing the motor so as to be responsive to heat derived and transmitted from the motor windings. Thus the overload control mechanism will trip to open the circuit in response to a rise in temperature alone. With the arrangement shown, the bimetal can be mounted in a position very close to the motor frame or windings so as to be responsive and sensitive to relatively minor variations in temperature. It is also to be noted that this construction provides for the starting relay and overload control mechanism all being mounted on a single frame which in turn is mounted on a raised pad within the housing which renders it relatively independent of variations due to expansion or contraction of the housing walls. There is thus provided a greater stability for the settings and adjustments after they are once made since the frame is relatively stationary thereafter.

While the form of embodiment of the present invention as herein described constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

I claim:

1. Switching mechanism comprising toggle mechanism including an elongated toggle arm, an elongated leaf spring member having one end connected with one end of the toggle arm, the free end of the spring member extending substantially parallelly along the side of the toggle arm, toggle spring means interposed between the free end of the spring member and the confronting end of the toggle arm, said spring means being pivoted on the confronting end of the toggle arm, a frame forming the sole support for the toggle mecha nism and having a part spaced outwardly but closely adjacent said one end of the toggle arm, and'a bimetallic leaf, said leaf having one end secured to the part and the other end thereof being connected with the toggle arm solely at a point spaced longitudinally from that end of the toggle arm which is connected with the spring member.

2. Switching mechanism comprising toggle mechanism including an elongated toggle arm, an elongated leaf spring member having one end connected with one end of the toggle arm, the free end of the spring member extending substantially parallelly along the side of the toggle arm, toggle spring means interposed between the free end of the spring member and the confronting end of the toggle arm, said spring means being pivoted on the confronting end of the toggle arm, a frame forming the sole support for the toggle mechanism and having a part spaced outwardly but closely adjacent said one end of the toggle arm, and a flexible bimetallic metal leaf, said leaf having one end secured to the part and the other end thereof being connected with the toggle arm solely at a point intermediate the ends of the toggle arm.

JOSEPH EDWARD KUMLER.

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